Abstr~ct.~o identify the responses of a predator to resource variation, age-specific fecundity and surviVorship were measured at several food levels for the sessile, predatory ciliate protozoan ~okop_hrya _lemnarum Stein. The major life history characteristics identified were: (I) a direct rela-tiOns~Jp exists between net reproductive rate and food level, (2) age-specific fecundity closely follows food.mta~e rat.e, (3) each embryo is endowed with a nutrient supply upon birth, and (4) an inverse relatiOnship exists between net reproductive rate-food level and life span. Totally starved individuals had the ~ongest mean life spans. Increased survival time at low food levels probably results from low ~etabohc rate between meals and a slowed accumulation of toxic waste products. Fecundity is directly rela~ed. t_o prey num~er and prey size. It is postulated that this set of adaptations acts to decrease ~anabihty of populatiOn size in a predator which cannot control its hunting rate and in which prey density must vary greatly during the lifetime of an individual.

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